Capsule-carrying sheets or webs

ABSTRACT

A capsule-carrying sheet or web such, for example, as is used in pressure-sensitive copying systems is produced by coating a surface of a base sheet or web with an aqueous coating mix which includes a rewettable binder material and a protective material. This coating is dried and then rewetted and a composite coating is formed by applying to the rewetted coating a coating of capsules. The composite coating is then dried.

United States Patent [191 Lewis Y Oct. 21, 1975 CAPSULE-CARRYING SHEETS0R WEBS v [75] inventor; Benjamin Stanley Lewis, Rhonnda,

Wales 73 .A's sig-nee: Wiggins Teape Research &

' Development, London, England [22 Filed: Jan. 29,1973

g 21 ,ApplnNoi: 327,790

[ 30] I Foreign Application Priority Data Jan. 31', 1972 UnitedKingdom4472/72 References Cited UNITED STATES PATENTS 3,565,666 2/l97l Phillips1 17/362 Primary Examiner-Th0mas .1. Herbert, Jr. Attorney, Agent, orFirmBurns, Doane, Swecker & Mathis [5 7] ABSTRACT A capsule-carryingsheet or web such, for example, as is used in pressure-sensitive copyingsystems is produced by coating a surface of a base sheet or web with anaqueous coating mix which includes a rewettable binder material and aprotective material. This coating is dried and then rewetted and acomposite coating is formed by applying to the rewetted coating acoating of capsules. The composite coating is then dried.

11 Claims, No Drawings lO/l972 Brown et al. ll7/36.4 X

CAPSULE-CARRYING SHEETS OR WEBS BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to capsule-carrying sheets or websand methods of producing such sheets or webs, and is particularly butnot exclusively concerned with capsule-carrying sheets or webs for usein pressuresensitive copying systems.

2. Description of the Prior Art The art of encapsulation has in recentyears achieved considerable commercial importance since encapsulationprovides a method of maintaining a reactive material in an inert stateby providing a non-reactive capsule wall between the reactive materialand its surroundings. Encapsulation also enables the handling propertiesof solids to be conferred on liquids and gases.

It is known to encapsulate, for example, dyes, inks, chemical reagents,pharmaceuticals, flavourings, pesticides, herbicides and in fact anymaterial which can be dissolved, suspended-or otherwise constituted inor as a liquid internal phase enclosed within a capsule wall. Thecapsule serves to maintain the internal phase in its liquid, or someother converted form, at least until the internal phase is released byrupture, melting, dissolving or other removal of the capsule wall, oruntil the internal phase is caused to diffuse out through the capsulewall.

Various methods of encapsulation are well known, the most commonly usedmethods involving either a coacervation reaction, a precipitationreaction, or a polymerisation reaction.

A disadvantage of capsules produced by known methods is that they arenot sufficiently inherently strong to prevent accidental rupturethereof, this being a particular disadvantage, in pressure-sensitivecopying systems where accidental rupture of capsules can result inundesirable marking of the copy sheet.

In order to increase the resistance of a capsulecarrying sheet or web,for use in a pressure-sensitive copying system, against accidentalrupture of the capsules, it is known to coat a protective material inthe form of cellulose fibres onto the sheet or web with the capsules,the protective material subsequently affording protection for thecapsules against accidental rupture while still allowing rupture thereofby localised pressure from for example, writing, typing or printing onthe sheet or web.

In British Pat. No. l,252,858 there is described another method ofaffording protection against accidental rupture of capsules in apressuresensitive copying system, in which method the previouslydescribed cellulose fibres are replaced, at least in part, by adifferent protective material in the form of granules of starch. Starchgranules said to be suitable include those produced from wheat,potato,-sago, tapioca, rice and arrowroot.

It known methods of producing a capsule-carrying sheet or web alsocarrying cellulose fibres as protective material for the capsules, thecapsules and cellulose fibres are coated together onto a base sheet orweb in admixture with a gelatinised starch solution which is to serve asa binder between the capsules and cellulose fibre, and the base sheet orweb. The sheet or web produced thus carries a coating includingcapsules, a protective material for protecting the capsules, i.e. thecellulose fibres, and a binder for the capsules and the protectivematerial i.e. the gelatinised starch solution.

A disadvantage of known methods of producing a capsule-carrying sheet orweb, in which the capsules are coated onto a base sheet or web inadmixture with a binder material and a protective material, is that thebinder material tends to form a film over the capsules, which film caninterfere with the required release of the internal phase of thecapsules on rupture of the capsules.

A further disadvantage of such known methods is that the binder materialgives the single coating mix used a relatively high viscosity, and thusthe coating mix must be coated at a relatively low solids concentration,the sheet or web thus having a relatively high moisture content aftercoating.

SUMMARY According to this invention a method of producing acapsule-carrying sheet or web comprising a base sheet or web having on asurface thereof a coating containing capsules, protective material forprotecting the capsules against accidental rupture, and a bindermaterial serving to bind the capsules and protective material to thebase sheet or web, comprises the steps of:

a. forming a first coating on a surface of a base sheet or web byapplying to the surface an aqueous coating mix including a rewettablebinder material and a protective material;

b. drying the first coating;

c. rewetting the dried first coating;

d. forming a composite coating by applying a coating of capsules to therewetted first coating; and

e. drying the composite coating.

Preferably steps 0 and d are carried out simultaneously by applying tothe dried first coating an aqueous emulsion of capsules. Otherwise,steps 0 and d can be carried out consecutively, the capsules beingapplied in dry form, for example by spraying.

The mechanism by which the method of the invention operates is simple.The binder material applied at step a is rewetted at step c and thenafter drying at step e serves to bind the capsules and protectivematerial to the base sheet or web.

Any suitable rewettable binder material can be used,

and examples of such binder material are dextrine, polyvinyl alcohol, ora mixture of dextrine and polyvinyl alcohol.

The protective material can be the commonly used cellulose fibres, orotherwise can be a granular polymeric material or, preferably, starchgranules, as described above.

Preferably the base sheet or web is calendered between steps b and c ofthe method of the invention. Calendering considerably reduces theroughness of the coated sheet or web produced at step a, but rewettingof the coated surface at step 0 causes the coated surface to regenerate,but not completely, towards that existing prior to calendering.

The method of the invention, in addition to overcoming the disadvantagesof known methods described above, has the advantage that the bindermaterial/protective material coating can easily be applied using a sizepress on the machine on which the base sheet or web (which will normallybe paper) is made. Further, a relatively high solids concentration canbe used for the aqueous dispersion of capsules, if used, and thus dryingof th sheet or web after application of the emulsion is simplified, andsince less water is applied to the sheet or web during application ofthe dispersion appearance defects such as cockle, ribbing, curl, etc.,all off which are related to the moisture content of the sheet or web,are reduced.

The aqueous dispersion of capsules, if used, can be applied by any meansknown for applying capsule coatings, for example by means of anair-knife coater.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now bedescribed by way of example with reference to specific workings thereofon a laboratory scale in relation to pressure-sensitive copying systemsof the kind in which a colourless, chromogenic material of basicreactant chemical properties held in solution in an oily solvent inmicrocapsules is reacted, upon rupturing of the microcapsules by appliedpresbelow 30C and 5 g. of unburst arrowroot starch granulesapproximately 25 pm in size were then dispersed in the solution.

The suspension thus formed was applied as a surface size by means of aMeyer rod to one side of a 49 g/m base paper to give a coating weight ofapproximately 1.3 to 2.2 g/m The sized base paper was then dried, andcalendered on a laboratory calender.

Samples of the base paper, and the sized base paper before and aftercalendering were tested, using standards tests, for thickness andBendtsen roughness.

Raw capsule dispersion (i.e. dispersion containing only capsules) wasthen coated onto the coated side of samples of the calendered sized basepaper using a Meyer rod, and the capsule-carrying samples thus producedwere, after drying, tested using standard tests for roughness,thickness, frictional smudge intensity, calender intensity and adhesion.

The results of the tests were as shown in the following Table I:

TABLE I Physical or Functional Property Tested Test Method Units MeanResult Range of Results Base paper thickness S.I.G. um 65.0 (62.5 to67.5) Base paper roughness Bendtsen ml/min 200 160 to 220) Sized basepaper thickness before calendering S.I.G. pm 80.0 (75.0 to 82.5) Sizedbase paper roughness before calendering Bendtsen ml/min 1350 l 100 to1650) Sized base paper thickness after calendering S.l.G. urn 67.0 (62.5to 72.5) Sized base paper roughness after calendering Bendtsen ml/min205 130 to 300) Sized base paper thickness after coating S.I.G. um 77.5(75.0 to 77.5) with capsules Sized base paper roughness after coatingBendtsen ml/min 405 (300 to 500) with capsules Frictional SmudgeIntensity obtained from Bausch & Lomb Refl. 82.6 (76.0 to 88.3)capsule-coated samples Calender Intensity obtained from capsule- Bausch& Lomb Refl. 61.6 (52.0 to 69.0) coated samples Adhesion incapsule-coated samples Visual 60 Estimated capsule coating weightSubstance g/rn 3.4 2.9 to 4.3

Measurements sure, with a coreactant material, such as attapulgiteEXAMPLE II clay, acid treated montmorillonite clay, or particles of anoil-soluble, acidic, phenolic, polymeric material, to providedistinctive coloured marks. The microcapsules can be carried on onesurface of a transfer sheet, known as a CB sheet, and the coreactantmaterial carried on one surface of a separate record sheet, known as aCF sheet, and the invention will be described in relation to such asystem.

Otherwise, the microcapsules and the co-reactant material can be carriedtogether on the same surface of a single sheet.

In working the invention as hereinafter described the capsules used wereapproximately 12 pm in size, and had walls of gelatin and gum arabicenclosing an internal phase comprising the dye substances crystal violetlactone and benzoyl leuco methylene blue dissolved in a dibenzylbenzenesadmixture, and diluted with kerosene. However, many different kinds ofcapsules are known which could otherwise be used.

EXAMPLE 1 A solution was formed by adding 5 g. of dextrine to 150 mls.of hot water. The solution was left to cool to A solution was formed byslowly adding 5 g. of Elvanol 52-22 (Registered Trade Mark) polyvinylalcohol to mls. of cold water and then heating the dispersion formed toincrease the rate of solution. The solution was left to cool to below30C and 5 g. of unburst arrowroot starch granules approximately 25 pm insize were then dispersed in the solution.

The suspension thus formed was applied as a surface size by means of aMeyer rod to one side of a 49 g/m base paper to give a coating weight ofapproximately 1.8 to 2.2 glm The sized base paper was then dried, andcalendered on a laboratory calender.

The same tests as in Example I were than applied to samples of the basepaper, and the sized base paper before and after calendering.

Raw capsule dispersion was then coated onto the coated side of samplesof the calendered sized base paper, as in Example I, and thecapsule-carrying samples thus produced were, after drying, subjected tosome of the tests detailed in Example I.

The results of the tests were as shown in the following Table II:

TABLE II Physical or Functional Property Tested Method Unit Mean ResultRange of Results Base paper thickness S.I.G. um 65.0 (62.5 to 67.5) Basepaper roughness Bendtsen ml/min 200 to 220) Sized base paper roughnessbefore calendering Bendtsen ml/min 1500 1450 to 1600) Sized base paperroughness after calendering Bendtsen ml/min 340 (250 to 400) Sized basepaper roughness after coating Bendtsen ml/min 450 (400 to 650) TAB LE 11Continued Physical or Functional Property Tested Method Unit Mean ResultRange of Results Frictional Smudge Intensity obtained fromcapsule-carrying samples Bausch & Lomb Refl. 92.2 (91.4 to 94.0)

Calender Intensity obtained from capsulecarrying samples Bausch & LombRefl. 53.6 (51.2 to 63.0)

Adhesion in capsule-coated samples Visual 100 Estimated capsule coatingweight Substance g/m 4.0 (3.4 to 4.6)

Measurements EXAMPLE III A first solution was formed by slowly adding0.5 g. of Elvanol 5222 (Registered Trade Mark) polyvinyl alcohol to 50mls. of cold water and then heating the dispersion formed to increasethe rate of solution.

A second solution was formed by adding 4.5 g. of dextrine to 100 mls. ofhot water.

The first and second solutions were then mixed and the resultingsolution left to cool to below 30C. 5 g. of unburst arrowroot starchgranules approximately um in size were than dispersed in the solution.

The suspension thus formed was applied as a surface size by means of aMeyer rod to one side of a 49 g/m base paper to give a coating weight ofapproximately 1.2 to 2.3 g/m The sized base paper was then dried andcalendered on a laboratory calender. The same tests an in Example I and11 were then applied to samples of the base paper, and the sized basepaper before and after calendering.

Raw capsule dispersion was then coated onto the coated side of samplesof the calendered sized base paper, as in Examples 1 and I1, and thecapsule-carrying samples thus produced were, after drying, subjected tothe same tests as the similar samples of Example 11.

The results of the tests were as shown in the following Table 111:

Background reflectance x X00 a value of indicating no smudging at all;the lower the value, the more the smudging, that is the poorer theprotection against accidental rupture of the capsules byhorizontally-applied pressures.

Calender Intensity Test A capsule-carrying sample and a sta' dard CFsheet (as described above) are superposed with their coated surfaces incontact and a strip of the two sheets then passed between two rollers.After a waiting period the reflectance of the coloured mark thus formedon the CF sheet and the reflectance of the background around thecoloured mark are measured with an opacimeter. The Calender Intensity orCl value of the capsule carrying sample is then determined from theequation:

Coloured mark reflectance I I Background reflectance a value of 100indicating no visible mark and thus the lower the value the moredistinct the coloured mark.

TABLE III Physical or Functional Property Tested Method Units MeanResult Range of Results base paper thickness S.l.G. p.111 65.0 62.5 to67.5 base paper roughness Bendtsen ml/min 200 to 220) sized base paperroughness before calendering Bendtsen ml/min 1500 1300 to 1650) s zedbase paper roughness after calendering Bendtsen ml/min 290 (230 to 350)sized base paper roughness after coating with Bendtsen ml/min 430 (400to 550) capsules (73.4 to 86.5) Frictional Smudge Intensity obtainedfrom Bausch & Lomb Refl. 79.2 capsule-carrying samples CalenderIntensity obtained from capsule- Bausch & Lomb Refl. 48.8 (45.1 to 52.0)carrying samples Adhesion in capsule-coated samples Visual 70+ Estimatedcapsule coating weight Substance g/m 4.2 (3.9 to 4.5)

Measurements The three most important tests of those mentioned above, towhich the capsule-carrying sheets or webs produced in the'abovedescribed Examples 1, II and III were subjected are the frictionalsmudge intensity test, the calender intensity test, and the adhesiontest and these tests will now be briefly described.

Frictional Smudge Intensity Test Adhesion Test A standard piece of blackcloth is laid on the coated surface of a capsule-carrying sample; aweight is placed on the cloth and the cloth is then dragged across thecoated surface of the capsule-carrying sample. The pattern thus producedon the cloth is then visually compared with a set of number standards, avalue of 60 or above indicating acceptable adhesion of the coating onthe capsule-carrying sample to the base paper.

Although the method of this invention has been described above inrelation to only laboratory workings thereof, no difficulty isexperienced in scaling up the described Examples for commercialproduction of capsule-carrying sheets or webs.

I claim:

1. A method of producing a capsule-carrying sheet or web comprising abase sheet or web having on a surface thereof a composite coatingcontaining capsules, protective material for protecting the capsulesagainst accidental rupture, and a binder material serving to bind thecapsules and protective material to the base sheet or web, comprisingthe steps of:

a. forming a first coating on a surface of a base sheet or web byapplying to the surface an aqueous coating mix consisting essentially ofa rewettable binder material and a protective material;

b. drying the first coating;

c. rewetting the dried first coating;

d. forming a composite coating by applying a coating consistingessentially of capsules to the rewetted first coating; and

e. drying the composite coating.

2. A method as claimed in claim 1, in which steps (c) and (d) arecarried out simultaneously by applying to the dried first coating anaqueous dispersion of capsules.

3. A method as claimed in claim 1, in which the capsules are applied indry form.

4. A method as claimed in claim 1, in which the binder material isselected from the group consisting of dextrine, polyvinyl alcohol, or amixture of dextrine and polyvinyl alcohol.

5. A method as claimed in claim 1, in which the protective material isselected from the group consisting of cellulose fibres, granularpolymeric material, or starch granules.

6. A method as claimed in claim 4, in which the protective material isselected from the group consisting of cellulose fibres, granularpolymeric material, or starch granules.

7. A method as claimed in claim 1, in which the base sheet or web iscalendered between steps (b) and (c).

8. A method according to claim 2, in which the base sheet or web is a 49g/m paper, the aqueous coating mix applied thereto consists of asuspension formed by preparing a solution of 5g of dextrine in 150 mlsof hot water, cooling the solution to below 30C, dispersing in thecooled solution 5g of unburst arrowrrot starch granules having a size ofapproximately 25 um and the suspension is applied to the paper toprovide thereon a coating weight of approximately 1.3 to 2.2 glm 9. Amethod according to claim 2, in which the base sheet or web is a 49 g/mpaper, the aqueous coating mix applied thereto consists of a suspensionformed by slowly adding 5g of polyvinyl alcohol to 150 mls of coldwater, accelerating the rate of solution by heating the dispersion soformed, cooling the solution to below 30C, dispersing in the cooledsolution 5g of unburst arrowroot starch granules having a size ofapproximately 25 um, and the suspension is applied to the paper toprovide thereon a coating weight of approximately 1.8 to 2.2 g/m 10. Amethod according to claim 2, in which the base sheet or web is a 49 g/mpaper, the aqueous coating mix applied thereto consists of a suspensionformed by preparing a first solution by slowly adding 0.5g of polyvinylalcohol to 50 mls of cold water, accelerating the rate of solution byheating the dispersion so formed, preparing a second solution by adding4.5g of dextrine to mls of hot water, mixing the first and secondsolutions, cooling the resulting solution to below 30C, dispersing inthe cooled solution 5g of unburst arrow root starch granules having asize of approximately 25 pm, and the suspension is applied to the paperto provide thereon a coating weight of approximately 1.2 to 2.3 g/m 11.A method of producing a capsule-carrying sheet or web comprising a basesheet or web having on a surface thereof a composite coating containing(a) a binder material, (b) protective material, and (0) capsules, saidprotective material protecting said capsules against accidental rupture,and said binder material serving to bind said capsules and saidprotective material to said base sheet or web, which method consistsessentially of the steps of:

a. forming a first coating on a surface of a base sheet or web byapplying to the surface an aqueous coating mix consisting essentially of(a) said binder material, said binder material being rewettable and selected from the group consisting of dextrin, polyvinyl alcohol, and amixture of dextrin and polyvinyl alcohol, and (b) said protectivematerial, said protective material being selected from the groupconsisting of cellulose fibers, granular polymeric material and starchgranules;

b. drying said first coating;

0. rewetting said dried first coating;

d. forming a composite coating by applying a coating consistingessentially of said capsules to said rewetted first coating; and

e. drying said composite coating.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION q Patent No.319141470 D d October 21, 1975 Inventor(5) Benjamin Stanley Lewis It iscertified that error appears in the above-identified patent a and thatsaid Letters Patent are hereby corrected as shown below:

At page 1, item No. [73] "Wiggins Teape Research & Development" shouldread Wiggins Teape Research & Development Limited Signed and Sealed thiseighteenth Day of May 1976 a {SEALI A nest:

v RUTH C. MiSON C. MARSHALL DANN Q Amstmg ()jjm'r (nmmissimu'rnj'lalenrs and Trademarks

1. A METHOD OF PRODUCING A CAPSULE-CARRYING SHEET OR WEB COMPRISING ABASE SHEET OR WEB HAVING ON A SURFACE THEREOF A COMPOSITE COATINGCONTAINING CAPSULES, PROTECTIVE MATERIAL FOR PROTECTING THE CAPSULESAGAINST ACCIDENTAL RUPTURE, AND A BINDER MATERIAL SERVING TO BIND THECAPSULES AND PROTECTIVE MATERIAL TO THE BASE SHEET OR WEB, COMPRISINGTHE STEPS OF, A. FORMING A FIRST COATING A SURFACE OF A BASE SHEET ORWEB BY APPLYING TO THE SURFACE AN AQUEOUS COATING MIX CONSISTINGESSENTIALLY OF A REWETTABLE BINDER MATERIAL AND A PROTECTIVE MATERIAL,B. DRYING THE FIRST COATING, C. REWETTING THE DRIED FIRST COATING, D.FORMING A COMPOSITE COATING BY APPLYING A COATING CONSISTING ESSENTIALLYOF CAPSULES TO THE REWETTING FIRST COATING, AND E. DRYING THE COMPOSITECOATING.
 2. A method as claimed in claim 1, in which steps (c) and (d)are carried out simultaneously by applying to the dried first coating anaqueous dispersion of capsules.
 3. A method as claimed in claim 1, inwhich the capsules are applied in dry form.
 4. A method as claimed inclaim 1, in which the binder material is selected from the groupconsisting of dextrine, polyvinyl alcohol, or a mixture of dextrine andpolyvinyl alcohol.
 5. A method as claimed in claim 1, in which theprotective material is selected from the group consisting of cellulosefibres, granular polymeric material, or starch granules.
 6. A method asclaimed in claim 4, in which the protective material is selected fromthe group consisting of cellulose fibres, granular polymeric material,or starch granules.
 7. A method as claimed in claim 1, in which the basesheet or web is calendered between steps (b) and (c).
 8. A methodaccording to claim 2, in which the base sheet or web is a 49 g/m2 paper,the aqueous coating mix applied thereto consists of a suspension formedby preparing a solution of 5g of dextrine in 150 mls of hot water,cooling the solution to below 30*C, dispersing in the cooled solution 5gof unburst arrowrrot starch granules having a size of approximately 25 mand the suspension is applied to the paper to provide thereon a coatingweight of approximately 1.3 to 2.2 g/m2.
 9. A method according to claim2, in which the base sheet or web is a 49 g/m2 paper, the aqueouscoating mix applied thereto consists of a suspension formed by slowlyadding 5g of polyvinyl alcohol to 150 mls of cold water, acceleratingthe rate of solution by heating the dispersion so formed, cooling thesolution to below 30*C, dispersing in the cooled solution 5g of unburstarrowroot starch granules having a size of approximately 25 m, and thesuspension is applied to the paper to provide thereon a coating weightof approximately 1.8 to 2.2 g/m2.
 10. A method according to claim 2, inwhich the base sheet or web is a 49 g/m2 paper, the aqueous coating mixapplied thereto consists of a suspension formed by preparing a firstsolution by slowly adding 0.5g of polyvinyl alcohol to 50 mls of coldwater, accelerating the rate of solution by heating the dispersion soformed, preparing a second solution by adding 4.5g of dextrine to 100mls of hot water, mixing the first and second solutions, cooling theresulting solution to below 30*C, dispersing in the cooled solution 5gof unburst arrowroot starch granules having a size of approximately 25m, and the suspension is applied to the paper to provide thereon acoating weight of approximately 1.2 to 2.3 g/m2.
 11. A method ofproducing a capsule-carrying sheet or web comprising a base sheet or webhaving on a surface thereof a composite coating containing (a) a bindermaterial, (b) protective material, and (c) capsules, said protectivematerial protecting said capsules against accidental rupture, and saidbinder material serving to bind said capsules and said protectivematerial to said base sheet or web, which method consists essentially ofthe steps of: a. forming a first coating on a surface of a base sheet orweb by applying to the surface an aqueous coating mix consistingessentially of (a) said binder material, said binder material beingrewettable and selected from the group consisting of dextrin, polyvinylalcohol, and a mixture of dextrin and polyvinyl alcohol, and (b) saidprotective material, said protective material being selected from thegroup consisting of cellulose fibers, granular polymeric material andstarch granules; b. drying said first coating; c. rewetting said driedfirst coating; d. forming a composite coating by applying a coatingconsisting essentially of said capsules to said rewEtted first coating;and e. drying said composite coating.